Pressure dropping as heating switched on

[turner89]

Hi all

Having a few issues with the boiler.

The pressure drops as soon as the heating is switched on (see video).

I’ve checked for leaks and can’t spot anything. There are no damp or wet patches on ceilings and I’ve ran some leak sealer through the system too. I’m topping the system up almost daily at the moment.

Any ideas on what this might be? Trying to avoid calling a plumber out but that seems the obvious route at this point.

Cheers

 

[ianmcd]

you should never have added leak sealer, it destroys boilers, all your guage is shownig is that the pump is running and the pressure guage sensor is connected to the negative side of the pump

 

[turner89]

you should never have added leak sealer, it destroys boilers, all your guage is shownig is that the pump is running and the pressure guage sensor is connected to the negative side of the pump

Thanks. Any idea why the pressure continues to drop when the heating is switched on? Currently its shot up to about 3 bars but when turned off will drop back to 1.5. And then overnight will continue to fall once again.

 

[oldbutnotdead]

Check the pressure relief valve, see if that's discharging (freezer bag tied round it is the usual trick).
But if the pressure isn't dropping all the way to zero when it's running and it rebounds back to where it was when the boiler is off then there is no problem, you may want to think about flushing the leak sealer out somehow before it blocks something critical

 

[ianmcd]

Your expansion vessel needs re-charging

 

[oldbutnotdead]

Thanks. Any idea why the pressure continues to drop when the heating is switched on? Currently its shot up to about 3 bars but when turned off will drop back to 1.5. And then overnight will continue to fall once again.

Water gets hot, water expands, pressure increases. Water cools down, water contracts, pressure reduces. Contracts more (so pressure reduces more) as it cools down overnight. Yeah EV

 

[turner89]

Thanks all.

So from here, flush the leak sealer out and re-charge the expansion vessel.

Cheers!

 

[Harry Bloomfield]

flush the leak sealer out and re-charge the expansion vessel.

Don't forget to add the inhibitor, when you refill after flushing.

 

[Madrab]

Water gets hot, water expands, pressure increases, expansion vessel (EV) should absorb the pressure increase if pre-charged properly unless the it has lost its pre-charge, in that case the system pressure rises too much, reaches the pressure release valve's opening setting, it opens and releases water and the pressure drops. Water cools down, water contracts, pressure reduces, as water has been now release through the PRV there isn't enough to sustain system pressure and overnight the pressure drops to 0. Contracts more (so pressure reduces more) as it cools down overnight. Yeah EV EV needs re-charged or replaced if membrane compromised

 

[oldbutnotdead]

Oh yes, forgot that bit (that if ev was working properly pressure would stay pretty constant), curse these newfangled modern things

 

[Harry Bloomfield]

Oh yes, forgot that bit (that if ev was working properly pressure would stay pretty constant), curse these newfangled modern things

It's the pump suction starting..

 

[Madrab]

all your guage is shownig is that the pump is running and the pressure gauge sensor is connected to the negative side of the pump